The plastic window-film coating is mainly applied in the two categories of cars and buildings. The functions of window film coating by a coating include adjusting indoor visible intensity, reducing the irritation to eyes as well as blocking the UV and IR rays from the sun light. The reduction of outdoor light entrance can prevent the irradiation of harmful rays to the human body, lessen the possible damage to the interior decorations, reduce the entrance of IR rays and lower the indoor temperature to save energy.
The modern processes to produce window films include roller coating or metal sputtering. The process of metal sputtering utilizes the principles of electric field and magnetic field to evenly sputter the metal particles at high speed and high power onto a PET substrate with high tension to form a magnetron sputtering window film. However, such films are very expensive to produce and not affordable to the users. On the contrary, the conventional processes of roller coating have the merits of low production cost, good plastic adhesion and high transparency, etc. So far, most of window films available in the market are produced using the UV-curable roller coating process. The UV-curable coating is characterized by high curing speed, low production cost, excellent quality and convenience for mass production.
The UV curing is mainly shown on the outermost layer of window film. This layer of colorless UV coating functions to increase the surface hardness of PET substrate and enhance the scratch resistance to enable the plastic window film not to be worn during the daily uses. On the other surface of PET is the gluing layer whose function is to make the PET plastic film to adhere to the glass surface firmly. As per the application environments, the light transmittance of a window film can be adjusted in a range of 5%-90%. The existing coloring agents are mainly dyes which can be used to adjust the colors with the characteristics such as high transparency, convenient handling and low production cost. Thus, the dyes are widely applied in adjusting the color of window film. Although the dyes have the advantages as above, they tend to decompose and fade, especially in the environment exposed to strong UV radiation. Thus, the coloring agent of dye is usually added in the gluing layer of window film in the process of window-film production to prevent UV direct radiation. Moreover, the dye is poor in outdoor weather resistance. If used outdoors for long time, the window film tends to fade and lose some transparency and show a poor appearance. Thus, the window film will give a shortened service life. Moreover, the dye itself cannot provide the function of thermal insulation and UV blocking, etc. At the same time, the dyes are expensive and will cause serious pollution during production. Thus, the application of the dye-type window films is limited. Therefore, the field is expecting a window-film product with good weather resistance and some heat shielding and UV blocking.